Below is an Orpin Water cooled engine which has been produced by Mervyn Stratford. This engine is a replica of the ones produced by Reg Orpin, which were available in 1966. Mervyn has used this engine at several meetings scoring some satisfying results.

ON SEEING just how fast the opposition was going at the beginning of the season, Reg Orpin skipped the head scratching stage and set about making a new glycol-cooled two-fifty Greeves. All but the stubs of the cylinder fins were cut off and a light-alloy jacket was welded around the block. (The stubs were, of course, drilled to allow circulation of the glycol.) A modified LE Velocette radiator, holding 5.5 pints of glycol, was mounted behind the engine beneath the seat. Cooling air is fed to the rad by two pairs of pipes from the nose and from the sides of the fairing. Big attraction of the glycol cooling is a much more even working temperature and a cylinder less liable to distortion. Advantage of this has been taken to run the piston on closer clearances than standard and to boost the compression ratio way above the usual 9 to 1 by modifying the combustion chamber in the air-cooled cylinder head. Twin-plug ignition is used, with sparks supplied by two Swedish Stefa coils to two lOmm plugs. The mods, in conjunction with a new exhaust system and adapted porting, have paid off, for bench tests have shown usable power coming in 800 rpm earlier than previously and without any falling off of peak power over a prolonged period. Nine hours' benching have shown no weaknesses in the design. Extensive work on the frame has dropped the overall height by 2in, thereby giving a lower frontal area. This has necessitated re-vamping the footrest layout to give adequate cornering clearance. Orpin stresses that the engine is purely experimental and has no connection with Greeves. Rider will be Gordon Keith.

Right: Birds eye view, showing the pipes feeding air to the radiator. Second 'clock' on the fairing is the water temperature gauge.